1. Field of the Invention
This invention relates to a magnetic recording medium which has high output characteristics and a low noise level and is suitable for high-density recording.
2. Discussion of the Background
As the demand for higher recording density in magnetic recording media of a coated type has been increasing, multi-layered magnetic recording media of a coated type comprising a substrate having provided thereon a plurality of coating layers have been manufactured and sold as high-density recording media.
A magnetic recording medium having a lower magnetic layer containing tabular magnetic particles having a relatively small coercive force and an upper magnetic layer containing acicular magnetic particles is disclosed in Japanese Patent Laid-Open No. 8-180376. The disclosed magnetic recording medium is capable of recording short wavelength signals (e.g., 0.41 .mu.m) on the upper layer and long wavelength signals (e.g., 1.8 .mu.m) on the lower layer, thereby exhibiting excellent performance in recording and out-put characteristics over a full range of from long to short wavelengths. However, the latest demand for techniques of high-density recording keeps on increasing to create the necessity of using magnetic powder having a higher coercive force in the lower layer.
In producing a magnetic recording medium having tabular magnetic particles of relatively high coercive force in its lower layer, when a coating layer containing the tabular magnetic particles of high coercive force is subjected, while wet, to magnetic field orientation in the horizontal direction, the tabular magnetic particles react sensitively to the magnetic field applied and are oriented with their plane having the longest diameter perpendicular to the surface of the magnetic recording medium. As a result, the surface of the lower magnetic layer, i.e., the interface between the lower magnetic layer and the upper magnetic layer, becomes rough, and the roughness is reflected to the surface roughness of the upper magnetic layer, i.e., the surface roughness of the magnetic recording medium. Therefore, it is difficult to reduce the surface roughness of a magnetic recording medium (e.g., to 3 nm or smaller) to achieve a high recording density merely by displacing tabular magnetic particles with those having a high coercive force in the lower magnetic layer.